Is it possible to connect a Bluetooth keyboard as a game controller to an iPad?

it's possible to connect a bluetooth keyboard just about all of them, if

you can use the keyboard to control games depend on if the game support it-

A Bluetooth keyboard can be easily paired and used with iPad:

https://www.imore.com/how-use-bluetooth-keyboard-iphone-and-ipad

Game support for an external keyboard will be App specific.